Ginkgo

The Ginkgo is a living fossil, with
fossils recognisably related to modern Ginkgo from
the Permian, dating back 270 million years.
The most plausible ancestral group for the order
Ginkgoales is the Pteridospermatophyta, also known
as the "seed ferns," specifically the
order Peltaspermales. The closest living relatives
of the clade are the cycads, which share with the
extant G. biloba the characteristic of motile sperm.
Fossils attributable to the genus Ginkgo first appeared
in the Early Jurassic, and the genus diversified
and spread throughout Laurasia during the middle
Jurassic and Early Cretaceous. It declined in diversity
as the Cretaceous progressed, and by the Paleocene,
Ginkgo adiantoides was the only Ginkgo species left
in the Northern Hemisphere while a markedly different
(and poorly documented) form persisted in the Southern
Hemisphere. At the end of the Pliocene, Ginkgo fossils
disappeared from the fossil record everywhere except
in a small area of central China where the modern
species survived. It is doubtful whether the Northern
Hemisphere fossil species of Ginkgo can be reliably
distinguished. Given the slow pace of evolution
and morphological similarity between members of
the genus, there may have been only one or two species
existing in the Northern Hemisphere through the
entirety of the Cenozoic: present-day G. biloba
(including G. adiantoides) and G. gardneri from
the Paleocene of Scotland.

Modern-day G. biloba grows best in environments
that are well-watered and drained, and the extremely
similar fossil Ginkgo favored similar environments:
the sediment record at the majority of fossil Ginkgo
localities indicates it grew primarily in disturbed
environments along streams and levees. Ginkgo therefore
presents an "ecological paradox" because
while it possesses some favorable traits for living
in disturbed environments (clonal reproduction)
many of its other life-history traits (slow growth,
large seed size, late reproductive maturity) are
the opposite of those exhibited by modern plants
that thrive in disturbed settings.

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